1. Field of the Invention
This invention relates generally to the field of rigid disc drive data storage devices and more particularly to a process for making a one-piece flexure assembly for supporting the read/write heads of the disc drive.
2. Brief Description of the Prior Art
Disc drives of the type known as "Winchester" disc drives are well known in the industry. Such disc drive data storage devices typically contain a stack of rigid discs coated with a magnetic medium on which digital information is stored in a plurality of circular concentric tracks. The storage and retrieval of data--also called "writing" and "reading", respectively--is accomplished by an array of heads, usually one per disc surface, which are mounted on an actuator mechanism for movement from track to track. The most common form of actuator used in the current generation of disc drive products is the rotary voice coil actuator, which uses a voice coil motor (VCM) coupled via a pivot mechanism to the heads to access data on the disc surfaces. The structure which supports the heads for this movement is referred to as a head/gimbal assembly, or HGA.
The HGA in a typical disc drive consists of three components:
1. a slider, which features a self-acting hydrodynamic air bearing and an electromagnetic transducer for recording and retrieving information on a spinning magnetic disc. Electric signals are sent to and received from the transducer via very small twisted copper wires;
2. a gimbal, which is attached to the slider and is compliant in the slider's pitch and roll axes for the slider to follow the topography of the disc, and is rigid in the yaw and in-plane axes for maintaining precise slider positioning, and;
3. a load beam, which is attached to the gimbal and to a mounting arm which attaches the entire assembly to the actuator. The load beam is compliant in the vertical axis to, again, allow the slider to follow the topography of the disc, and is rigid in the in-plane axes for precise slider positioning. The load beam also supplies a downward force that counteracts the hydrodynamic lifting force developed by the slider's air bearing.
Since the introduction of the first Winchester disc drive, the physical size of the slider has been progressively reduced, first from the original Winchester head to the so-called "mini-Winchester", and more recently to the 70 and 50 Series heads, which are 70% and 50% the size, respectively, of the mini-Winchester slider. While these size reductions are significant, the overall vertical dimension of the HGA has been dictated more by the slider-supporting mechanism than by the size of the slider itself.
The load beam and gimbal comprise an assembly generally known as a head suspension, head flexure, or simply a flexure. An example of such a flexure is described in U.S. Pat. No. 4,167,765.
Historically, the gimbal and load beam are fabricated discretely. The gimbal and load beam pieces are realized by chemically etching 300 series stainless steel foil into the desired shape, and then the two pieces are attached by means of laser welding.
The general technology trend in disc drive data storage devices is continual shrinking of the physical size of the product while providing increased data storage capacity. The down-sizing of the product has required smaller components, especially the principal components such as discs, sliders and flexures. Additionally, disc drive designers seek to add capacity to their designs by incorporating as many discs as possible within defined package dimensions. As the number of discs in the unit increases, the spacing between the discs decreases, thus further driving the need for smaller sliders and flexures.
Another industry trend is to provide the user of disc drives with high data storage capacity at low cost. This requires developing improved data recording technology and finding lower cost ways of manufacturing the components of the disc drive.
The use of discrete gimbal and load beam components laser welded together, as shown in the '765 patent, has become problematic in disc drives of the current 2.5", 1.8" and 1.3" generations of disc drives. In such units, the flexures must become thinner in order to allow desirable close spacing of the discs, while the overlapping required to laser weld two discrete components necessitates increased thickness in the flexure.
Furthermore, the use of thinner gimbal and load beam components increases the likelihood of residual stress caused by the laser welding of the two components together. It has been found that laser welding produces residual tensile stress in the material local to the welds. This causes the flexure to distort. In the longitudinal direction, the flexure curls from the residual weld stress, and this makes it more difficult to fit the flexure between closely spaced discs during the manufacturing process. Further, if the welds are not placed symmetrically about the centerline of the flexure, the residual weld stress will cause a torsional distortion, or twisting, of the flexure. Such an flexure is undesirable since the twist will create a moment, or torque, on the slider's air bearing, causing unwanted changes in the flying attitude of the head, and potentially rendering the assembly unusable.
The welding process is also a substantial portion of the labor that goes into the manufacture of a flexure, and it would, thus, be advantageous to eliminate the practice of making discrete gimbals and load beams and welding the two together for cost reduction.
Since the gimbal and load beam components must overlap in flexures of existing art, the emphasis on reducing the thickness of the flexure assembly has most often focused on reducing the thickness of the individual gimbal and load beam components. The thickest area of the load beam is the region known as the rigid beam, which usually features flanges along the outer edge along the longitudinal axis of the flexure. U.S. Pat. No. 4,996,616 teaches how a pair of drawn ribs can provide reinforcement of the rigid beam section of the flexure. Unfortunately, the drawn pair of ribs of '616 requires that the flexure material be strained to exceedingly high levels. Such stain can introduce cracks in the drawn material, and high stresses in the material near the ribs.
Various attempts have been made to solve the problems inherent in welding a gimbal and load beam together by devising a flexure in which the gimbal and load beam are formed from a single piece of material and would thus require no welding. An example of such an integrated gimbal and load beam is presented in U.S. Pat. No. 4,245,267. A second example is known as the HTI Type 16, or T16, manufactured by Hutchinson Technology, Incorporated. Both of these flexures have a gimbal incorporated into the load beam and, of course, no gimbal-to-load beam welds. Both include a bonding surface on which adhesive is placed to secure attachment of the slider to the flexure. A plurality of beams, etched into the load beam, connects this bonding surface to the load beam portion of the flexure and provides the desired gimbal characteristics.
One failing of the flexure of the '267 patent and the T16 flexure relates to an element of flexure design commonly referred to as "load point". Simply stated, load point refers to the single point of contact where the downward force of the load beam is applied to the slider. Proper selection of this load point ensures that the forces related to the hydrodynamic air bearing of the slider are properly balanced. In prior art flexures such as the one described in the '765 patent, load point is developed by forming an upward-extending dimple in the gimbal bonding surface. The load beam contacts the spherical surface of this dimple at a single point to allow proper gimbal action. In the case of the '267 and T16 flexures, however, a well defined load point is not provided, and, thus, an undesirably wide range of variation in slider flying characteristics is associated with these types of flexure.
A second fundamental problem with the '267 and T16 types of flexures is that the downward force of the load beam is applied to the slider by placing the gimbal beams into bending mode, and the gimbal beams must therefore be stiff in bending mode. These same gimbal beams, however, must be compliant in bending mode to allow the proper gimballing action. This conflicting requirement results in designs that either work poorly as a gimbal or become deformed under load.
A third problem with the '267 and T16 flexures is that the slider bonding surface, in general, covers a large area over the center of the slider. The slider is attached to the flexure with an adhesive epoxy, and, in order to reduce the cure time of the adhesive, the assembly is usually heated in an oven. Since the slider and flexure are made of dissimilar materials with different coefficients of linear thermal expansion, thermally induced strains develop at the bond when the assembly cools. These strains can distort the slider and undesirably change the flatness of the air bearing surface of the slider, thus, once again, introducing unacceptably wide variation into the flying characteristics of the heads.
A need clearly exists for an improved slider-supporting flexure which reduces the overall vertical height of the HGA, and which can be manufactured in a simple, cost-effective manner.